During installation, service and maintenance of powered equipment, service personnel such as electricians must assure that the equipment is isolated from its power source. Examples of such equipment include, but are not limited to, high voltage power supplies, milling machines, boilers, electron microscopes, elevators, fan systems, and lasers. Although the power source is usually electrical, other power sources such as mechanical, hydraulic, pneumatic, chemical, and thermal may be involved.
When the power source and the equipment are in the same room, isolation is not difficult. However, more often than not, the power source, e.g. breaker box, is located relatively far away from the equipment. Thus, it is possible that after the equipment is isolated at the power source it may be inadvertently powered on by other personnel who do not know that the equipment was intentionally powered off. Work situations where unexpected energizing or start-up can occur include new construction, installation or set-up of equipment, and the adjustment, inspection, maintenance, repair, and service of machines and equipment.
“Lock-out” and “Tag-out” refer to safe methods for the complete power isolation of equipment during maintenance or service work. OSHA regulations 29 CFR 1910.147 and 1926.416 require the use of locks or tags at control points such as breaker boxes as warning devices to ensure that personnel are not injured from accidental machine start-ups. While many lock-out and tag-out solutions perform well, none are fool proof. For example, tag-out solutions assume that all personnel can read the same language. Although lock-out solutions do not require literacy on the part of personnel, lock-outs are difficult to install and often require that the device to be locked is pre-equipped with a lock receiving apparatus. In addition, a lock-out may be bypassed intentionally or accidentally without the knowledge of the affected personnel.